Preparation Of Modified Aluminum Powder Encapsulated With Fluorine-silicon Polymers And Its Application

Aluminum powder is one of the widely used metal powder material due to its most readily available sources,cheapest and the processing technologies were simple,aluminum powder is mainly divided into flake aluminum powder and spherical aluminum powder.Flake aluminum powder has been widely used in coating,printing ink,plastic processing and other fields because of its"flip-flop"effect,metal luster and reflection effect.Flake aluminum powder have a large contact area with air,and high activity of aluminum atoms,so it is easy to be corrode by oxygen,which will damage the metallic luster of flake aluminum powder.In addition,flake aluminum powders with only silvery white color cannot meet the growing needs for colored special-effect pigments.Spherical aluminum powder has large specific surface area and high combustion enthalpy.When spherical aluminum powder is used in solid propellant,it can improve the specific impulse and combustion performance of propellant.Spherical aluminum powder is easily oxidized when it is exposed to air,and the surface is covered by alumina layer.The practical energetic applications of aluminum powders are often limited by dense oxide layers which form on their surface.Therefore,in order to solve the above problems,we need to carry out surface functional modification of flake aluminum powder and spherical aluminum powder before application.In this paper,the functional modification of flake aluminum powder and spherical aluminum powder is studied.On the one hand,the colored aluminum powder is prepared by coloring the flake aluminum powder with a bis（monochloro-s-triazine）reactive dye and then coating a layer of fluoropolymer film on the outside.The obtained colored aluminum powder has bright colors and greatly improved acid and alkali resistance;on the other hand,fluoropolymer single-layer coated spherical aluminum powder and fluoropolymer/silica double-layer coated spherical aluminum powder are separately prepared by coating the surface with fluoropolymer.The main research results are as follows:（1）Firstly,the sol-gel method was used.A layer of Si O₂ was coated on the surface of the flake aluminum powder with tetraethyl orthosilicate（TEOS）as the precursor,and3-aminopropyltriethoxysilane（KH550）was used for the modification of Si O₂ layer.Then the nucleophilic reaction method with bis（monochloro-s-triazine）reactive dye（KE-3B）as the colorant was used to color the flake aluminum powder.Finally,the in-situ polymerization method with trifluoroethyl methacrylate（TFEMA）as the monomer and trimethylolpropane trimethacrylate（TMPTMA）as the crosslinking agent was successfully used to coat a layer of fluoropolymer film on the reactive dye layer.A colored aluminum powder coated with a layer of fluoropolymer film and bis（monochloro-s-triazine）reactive dye was prepared.Scanning electron microscope（SEM）and X-ray photoelectron spectroscopy（XPS）were used to analyze the surface morphology and elements of colored aluminum powder.The results showed that the successful preparation of the colored aluminum powder coated with fluoropolymer and bis（monochloro-s-triazine）reactive dye.The alkali resistance test and spraying experiment were carried out.The results indicate that the obtained colored aluminum powder has bright colors and good alkali resistance to reach no reaction for 24 hours in 5 wt%lye.All the above results prove the excellent performance of the prepared colored flake aluminum powder.（2）In order to improve the combustion performance of spherical aluminum powder and meet the demand of solid propellant for high-energy metal fuel,Acrylic acid（AA）was used to modify the spherical aluminum powder,and then the in-situ polymerization method with trifluoroethyl methacrylate（TFEMA）as the monomer and trimethylolpropane trimethacrylate（TMPTMA）as the cross-linking agent was used to coat a dense fluoropolymer film on the surface of the spherical aluminum powder.The surface morphology and elements of fluoropolymer single-layer coated spherical aluminum powder were analyzed by Scanning electron microscope（SEM）and X-ray photoelectron spectroscopy（XPS）.The results showed that the spherical aluminum powder was successfully coated by fluoropolymer.The exothermic behavior and weight change of fluoropolymer single-layer coated spherical aluminum powder were characterized by simultaneous thermal analysis.It can be concluded that the fluoropolymer film plays an important role in the oxidation protective layer and oxidation assistant of the spherical aluminum powder.（3）In order to further meet the demand of solid propellant for high-energy metal fuel.The sol-gel method with tetraethyl orthosilicate（TEOS）as the precursor was used to coat a layer of Si O₂ on the surface of the spherical aluminum powder.Then a dense fluoropolymer film was in-situ polymerizd on the surface of the Si O₂ layer with trifluoroethyl methacrylate（TFEMA）as the monomer and trimethylolpropane trimethacrylate（TMPTMA）as the crosslinking agent.Fluoropolymer/silica double-layer coated spherical aluminum powder was obtained.Scanning electron microscope（SEM）and X-ray photoelectron spectroscopy（XPS）was used to analyze the surface morphology and elements of fluoropolymer/silica double-layer coated spherical aluminum powder,the results showed that the spherical aluminum powder was successfully coated with silica and fluoropolymer.The exothermic behavior and weight change of fluoropolymer/silica double-layer coated spherical aluminum powder were characterized by simultaneous thermal analysis.We can conclude that Si O₂/fluoropolymer double-layer coated spherical aluminum powder can be widely used in solid propellants in the future.